The pH and chloride microsensors were used to study propagation and repassivation of pits on pure aluminum in pH 11 NaCl solution. It was concluded that the pH inside a growing pit was around 2.7, and the chloride concentration was higher than the saturation concentration. After current to the pit was turned off, pH of the pit electrolyte stayed at 4.5 for 30 s before relaxing to pH 11. It was proposed that dissolution of salt film inside pits buffered pH of the pit electrolyte when the pit growth was terminated, and the dissolution of the salt film determined the pit repassivation behavior.